Erratic Tach Signal

Reply Subscribe

Thread Tools

Search this Thread

Apr 10, 2008 | 08:15 PM

89vette

Thread Starter

Melting Slicks

Joined: Aug 2000

Posts: 2,388

Likes: 42

From: Murrysville PA

Erratic Tach Signal

I have an issue with my 89 disco dash tach display. Sometimes it jumps all around and displays incorrect information. I discovered that if the tach wire coming off the distibutor is near the plug wires this will happen. I run MSD 8.5mm wires. Does this mean that my plug wires could be bad?

Apr 11, 2008 | 01:01 PM

vinnies87

Le Mans Master

Joined: Aug 2003

Posts: 9,884

Likes: 3

From: Magnolia Mississippi

St. Jude '03-'04-'05-'06-'07

check and/or replace tac filter - reference FSM

Apr 11, 2008 | 01:11 PM

Redeasysport

Le Mans Master

Joined: Dec 2004

Posts: 5,789

Likes: 8

From: Myrtle Beach SC

St. Jude Donor '05-'06

Quote:

Originally Posted by vinnies87

check and/or replace tac filter - reference FSM

Jun 7, 2011 | 01:55 PM

89vette

Thread Starter

Melting Slicks

Joined: Aug 2000

Posts: 2,388

Likes: 42

From: Murrysville PA

Didn't work.

Jun 7, 2011 | 02:39 PM

engle1147

Le Mans Master

Joined: Jul 2007

Posts: 5,043

Likes: 8

From: Tampa Florida

Quote:

Originally Posted by 89vette

Do any work (ignition related) to the car before the disco dash stuff started or did this problem just develope out of the blue?
How old are the plug wires?

You could:
Put the car in the dark, pop the hood, start the engine and look for arcs coming thru the plugwire insulation.
Check for good "ground" at the distributor connector (coil) & @ and to the distributor body (see if you can tighten the dizzy's hold down bolt at all).

Last edited by engle1147; Jun 8, 2011 at 11:03 AM.

Jun 7, 2011 | 02:56 PM

powerpigz-51

Drifting

Joined: May 2006

Posts: 1,428

Likes: 7

From: Chewelah Wa

Do you have a aftermarket coil? I installed a hypertech and my graph tach stopped reading properly.

Jun 7, 2011 | 04:32 PM

M.J.L.

Safety Car

Joined: Jul 2008

Posts: 3,966

Likes: 4

From: Made In America

St. Jude Donor '10-'11

Quote:

Originally Posted by powerpigz-51

Do you have a aftermarket coil? I installed a hypertech and my graph tach stopped reading properly.

Jun 7, 2011 | 04:47 PM

stevie1dr

Pro

Joined: Jun 2006

Posts: 508

Likes: 1

From: Miami Florida

go to Ekler's or Mid America and buy the tach filter and install it. This will solve the problem as I had the same bouncing tach, and the filter corrected the problem.

Steve